As the world today rapidly increases its demand of the fuels, energy shortage becomes one of the most challenging issues the human being is facing. Fossil fuels, which currently contribute more than 85% of the world's energy supply, are expected to be depleted in the following 30˜50 years. In addition, it is extensively believed that burning the fossil fuels is the major cause for global-warming and long term climate change leading to natural disasters, further pressing on the need for reductions in fossil fuel usage.
These possible near-future environmental disasters have attracted people's attention and resulted in a vast and growing interest in development of alternative renewable energy resources. Among the studies that have been done, hydrogen energy is considered as an alternative to fossils fuels as a source of energy, and is expected to have enormous growth potential as a result of recent advances in technology. Hydrogen is renewable, very flexible in conversion to other forms of energy, and no air pollutants or green house gases are produced from the combustion of hydrogen. In an idealistic, long-term vision, a hydrogen/electricity interchangeable energy source can provide power for all aspects of the energy economy such as transportation, industrial, and residential usage.
Traditionally, hydrogen gases are produced primarily via the processes of steam reforming methane and electrolysis of water. The former produces CO2 (a green house gas) that is released into the atmosphere, while the later uses electricity generated from fossil fuels.
In recent years, the alternative production method of using solar energy to produce hydrogen has triggered great interest. Specifically, photocatalytic water splitting using oxide semiconductors under irradiation has received great attention. A tremendous amount of research articles have recently been published on the topic, such as concerning the use of a titania-based photocatalyst, which is the most common material for hydrogen production, in photovoltaic cells, as well as in environmental decontamination. Thousands of studies are ongoing concerning improving the performance of this and other photocatalysts in two main areas: 1) quantum efficiency, such as oxide-doping and metals additions; and 2) solar efficiency, including anion doping, and physically/chemically implanting the transition metals in the photocatalyst. Yet, all the research currently being done contains many limitations and drawbacks including the small number of available photocatalysts, their limited efficiency, cost, and device life-time, which still remain unsolved up to this point.
As a result, it is highly desirable to develop a mature and commercially available technology for hydrogen production that can be put directly into application in daily usage.